Exhaust systems of internal combustion engines may include an exhaust-gas aftertreatment device comprising one or more catalytic converters, for example an oxidation catalytic converter. In order to function optimally, such exhaust-gas aftertreatment devices may, at least intermittently, function with an exhaust-gas temperature higher than that attained during normal engine operations. In one particular example, the exhaust temperature is increased by means of an exothermic reaction of unburned fuel contained within the exhaust-gas flow on an oxidation catalytic converter element.
It is known for the exhaust-gas flow to be enriched with fuel directly injected into an engine cylinder by means of a post-injection, which takes place after the combustion process. However, problems arise since some of the fuel injected may pass into and thin the engine oil that is used for lubricating the engine. Thereby, the lubricating action of the engine oil is diminished over time. Alternatively, the exhaust-gas flow may be enriched with fuel injected directly into the exhaust tract of the engine. For this purpose, an injection nozzle is provided for injecting the fuel at a relatively low pressure (e.g., 5 to 10 bar) directly into the exhaust-gas flow. In one example, the fuel injected may be sprayed onto a heating element that further assists with the fuel evaporation process before introduction into the exhaust-gas flow. However, adding an injection system of such design to a vehicle increases both the vehicle complexity and its overall cost. In another example, US 2011/0107740 A1 describes an internal combustion engine with direct injection means, wherein the exhaust system of the engine has a fuel cell such that a first cylinder is operated in lean-burn mode to deactivate the fuel injection and a second cylinder is operated with a rich mixture.
Herein, the inventors have recognized issues with the approaches above and describe methods for operating a first cylinder group without a compression and power stroke injection, but with an exhaust stroke injection while operating a second cylinder group with at least a compression stroke injection, where each of the exhaust stroke injection and compression stroke injection are greater than a threshold. Thereby, the system and methods may inject fuel to one or more cylinders during an exhaust stroke to heat the exhaust system while also injecting fuel during one or more compression strokes to power the vehicle drivetrain during the engine drive cycle. The methods according to the present disclosure therefore provide an alternative method and device for controlling the internal combustion engine in order to enrich the exhaust-gas flow with fuel. In one example provided, a four-stroke in-line applied-ignition engine operated in accordance with the present disclosure delivers a main injection of the fuel injection process into one or more cylinders during an exhaust stroke of the engine drive cycle. As such, no main injection occurs during a compression stroke of the cylinder since said main injection instead takes place during the exhaust stroke. Further, because the main injection takes place during the exhaust stroke, the amount of fuel supplied to the cylinder during said main injection is not necessarily available for generating power during the working stroke, which is referred to herein as the power (or expansion) stroke. In this sense, fuel injection within a cylinder is reduced and the cylinder is deactivated.
By virtue of the fact that the main injection takes place during the exhaust stroke of a cylinder, the mixture of fuel and air produced therein thus allows the exhaust-gas flow to be enriched with unburned fuel in a particularly simple and effective manner. Therefore, the exhaust-gas temperature at an oxidation catalytic converter element can be increased while the operation of the exhaust-gas aftertreatment device is enhanced. In particular, an additional injection system for injecting fuel into the exhaust system is not required, which reduces the overall cost and complexity of the engine system described herein. In addition, because one or more cylinders are sometimes operated with no main injection during a compression stroke, intake stroke or expansion stroke, enriching the exhaust-gas flow with fuel is particularly expedient since the fuel-air mixture is discharged into the exhaust tract. In this way, a fuel injection system can be designed to produce an adequate amount of fuel while also controlling the fuel injection with adequate precision.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.